1. Field of the Invention
The present invention relates to a cutter suitable for cutting a spiral groove on the outer periphery of a work such as an intermittent feed part.
2. Description of Prior Art
An intermittent feed mechanism has conventionally been known in which a screw-threaded member having a spiral groove on the outer periphery thereof is rotated by a predetermined angle so that a movable member engaging the spiral groove is reciprocated by a predetermined distance.
One example of such intermittent feed mechanism is the carriage transfer mechanism incorporated in the disk drive device covered by Japanese Patent Application No. 61-52357 filed by the subject applicant. An embodiment of the disk drive device disclosed in this application is the so called still video floppy device for recording/reproducing a still picture, an outline of which device will be explained hereunder with reference to FIGS. 10 through 16 of the accompanying drawings.
The disk drive device shown in the above figures comprises a frame 1, a slide plate 2 slidable vertically (See FIG. 10) on the upper part of the frame 1 and projections 6a and 6bprovided on the side surfaces of the frame 1 so as to engage cam grooves formed in side plates 2a and 2b of the slide plate 2 adjacent to side plates 3 and 4 of the frame 1. Further, within the frame 1, there are provided a holder 7 for retaining a disk cartridge, a motor 9 attached to the upper part of the frame 1 so as to rotate a turntable 8 and forming a disk drive mechanism together with the turntable, a carriage 10 holding a head 37 and carried in the radial direction of a disk (not shown) at the upper part of the frame 1, a carriage transfer mechanism 12 for transferring the carriage 10 through a stepping motor 11 and a rock-lever 14 capable of regulating the sliding position of the slide plate 2.
The carriage transfer mechanism 12 used in the disk drive mechanism forms itself a carriage transfer unit 20. As shown in FIG. 12 (an exploded perspective view) and FIG. 13 (a sectional view of an essential part), the carriage transfer unit 20 is mainly composed of a support plate 21, a stepping motor 11 and a screw-shaft 22. As will be clear from FIG. 12, the support plate 21 is bent in two stages so that the stepping motor 11 is mounted to the lower surface of a stepping motor mounting section 23 located above the bottom plate 16 of the frame 1 and the screw-shaft 22 is held between bearings 26 and 27 supported by side walls 24 and 25 on both ends of the support plate 21. Thus the screw-shaft 22 and the stepping motor 11 are integrally mounted to the support plate 21 thereby forming a single unit.
An intermittent drive screw 28 threaded on and around the screw-shaft 22 is the same as that disclosed in Japanese Utility Model Application No. 60-67564 filed by the subject applicant and as shown in FIGS. 14 through 16, it is provided with a number of axially displaced grooves 22a on the outer periphery thereof over a predetermined range. Each of the grooves 22a runs parallel to the perpendicular Y normal to the axis X (that is, the lead angle is zero=.theta..sub.2) and the bottom thereof is linear so that a spiral groove 22b is formed by the grooves 22a and a feed section 22c by which the carriage 10 is transferred by a predetermined pitch is formed at each of the portions where the adjoining grooves 22a connect to each other.
In the case of the carriage transfer unit 20 in which an engaging member 29 of the carriage 10 is caused to mate with the spiral groove (intermittent drive-screw) 22b of the screw-shaft 22, the carriage 10 travels in a predetermined direction in correspondence to the lead angle .theta..sub.1 when the engaging member 29 slides within the feed section 22c of the spiral groove 22b while when the engaging member 29 comes to the desired one of the grooves 22a forming the spiral groove 22b, the stepping motor 11 is de-energized to stop the movement of the carriage 10. Thus, the carriage 10 moves due to the existence of the feed sections 22c and can stop at desired one of the grooves 22a so that it can be fed intermittently. In this case, as the lead angle .theta..sub.2 of the screw-shaft 22 is zero within the groove 22a, even if the angle of rotation of the screw-shaft 22 should become displaced slightly, the stop position of the carriage 10 will be properly set to a high degree of accuracy.
The bearings 26 and 27 for supporting both ends of the screw-shaft 22 are pivot bearings which can rotatably support the ends of the shaft such that the end of the shaft on the side of the bearing 26 is urged toward the right in FIG. 13 by a compression spring 30 and the other end of the shaft on the side of the bearing 27 is adjusted of its position axially by an adjusting screw 31 embedded in the bearing 27. Further, the bearing 27 regulates the level of the carriage transfer unit 20 itself such that while it is supported by the side wall 25 of the support plate 21 as already mentioned, the end thereof in which the adjusting screw 31 is embedded is caused to project, as at 32, from the side wall 25 and the projection 32 is inserted into a support hole 33 in the side plate 4 of the frame 1.
A spur gear 34 fitted on the screw-shaft 22 meshes with a crown gear 36 fitted on the rotary shaft 35 of the stepping motor 11 fixed to the support plate 21 so that the stepping motion of the stepping motor 11 is transmitted to the screw-shaft 22 through the crown gear 36 and the spur gear 34, whereby the rotation of the stepping motor 11 is transmitted to the carriage 10 through the intermittent drive screw 28 to cause the carriage to advance straight step by step.
As described above, the disk drive device is designed to increase the accuracy of the stop position of the carriage 10 without the necessity of using a high-precision and expensive stepping motor, by forming on the outer periphery of the screw-shaft 22 the spiral groove 22b whose lead angle .theta..sub.2 becomes zero within the groove 22a. And in order to machine such spiral groove 22b, a cylindrical cutter 38 shown in FIG. 17 is used. The cutter 38 is provided on the outer periphery thereof eight cutting edges 38 which are arranged at equal intervals in the circumferential direction and displaced from one another by 1/8 inch in sequence in the axial direction. The use of such cutter is advantageous in that since the spiral groove 22b can be formed on the outer periphery of a work to be finished to the screw-shaft 22 by rotating the cutter and the work in the same direction, cutting is performed in a simple manner without using a specific and expensive screw cutting lathe or the like.